The present invention relates to a method of making an annular friction liner. More particularly, the invention relates to a friction liner in the form of an annular ring, which is either flat or in the form of a frustum of a cone. The device which is equipped with this liner is a clutch friction wheel or a disc brake, especially for an automatic gearbox associated therewith and typically operating in oil. Another application is that of a synchronising ring or cone in a manual gearbox, again typically working in oil. In general, such devices are part of a motor vehicle.
The invention relates especially to the manufacture of a friction liner of the type which is made from a friction material consisting of a mat of fibres impregnated with a thermosetting resin, such as is described in U.S. Pat. No. 5,807,518.
Various ways of making a flat annular friction liner are known, which include the steps of cutting out the friction liner either in one piece or in sections, but these methods involve excessively high, and costly, wastage.
In order to overcome this disadvantage, the invention, in a first aspect, provides a method of making a friction liner of generally annular form, characterised in that it consists in:
forming a straight strip of friction material having a width which is substantially equal to the required final width of the friction liner; and then
deforming the straight strip so as to configure the latter into a continuous annular ring.
The method preferably further includes receiving the strip of friction material, after the latter has been configured into a curved form, in a guide of complementary form.
The method preferably further consists in simultaneously trimming the circular edges of the annular strip after the latter has been configured into its circular configuration, so as to give an annular strip of constant predetermined width.
The method preferably further consists in cutting a sector of the annular strip after the latter has been configured into its circular form, the said sector, corresponding to one complete circumference, followed by the further step of joining together the adjacent ends of the strip.
According to a preferred feature of the invention, the straight strip of friction material is deformed into its curved form by passing it between two adjacent conical rolls with intersecting axes.
Preferably, the straight strip of friction material is made from a friction material which is adapted for equipping a friction device, and more particularly a clutch friction wheel or brake disc, the material consisting of a mat of fibres impregnated with a thermosetting resin.
More particularly, the friction material is preferably of a kind adapted for equipping a friction device working in a liquid medium, and more particularly a device such as a clutch friction wheel or brake disc, especially for an automatic gearbox or, associated therewith, a synchronising ring or cone of a manual gearbox.
The friction liner is an annular liner which may be flat or frusto-conical.
According to the invention in a second aspect, a generally annular friction liner is characterised in that it is made by a method according to the invention in its first aspect.
According to the invention in a third aspect, apparatus is provided for performing the method of the invention. The apparatus being characterised in that it includes a deformation or configuring station at which the straight strip of friction material is configured into its curved form. The configuring station comprising two adjacent conical rollers having intersecting axes which lie in a common plane at right angles to the plane in which the straight strip of friction material is advanced between the conical rolls.
The apparatus according to the invention preferably includes, upstream of the configuring station, a longitudinal tensioning station which comprises two cylindrical rolls having parallel axes lying in a common plane at right angles to the plane in which the straight strip of friction material is advanced between the cylindrical rolls.
Further features and advantages of the invention will appear more clearly on a reading of the following detailed description of some preferred embodiments of the invention, which are given by way of non-limiting example only and with reference to the accompanying drawings.